A charged particle beam apparatus for measuring and inspecting a sample having some parts in focus and other parts out of focus in an image due to the effect of the roughness of the sample surface is disclosed, in which in order to acquire a clear image of the whole or a predetermined area in the image, the focus adjustment conditions for each point in the area to be scanned by the charged particle beam are determined in advance, and the focus adjustment conditions thus determined are applied selectively to the patterns formed under the same fabrication conditions as the sample for which the focus adjustment conditions are determined.